Rocker mechanism



Aug- 1, 1967 J.1.MATTHEWS sssm ROCKEH MECHANI SM Filed sept. v, 1965faz@ 3 L 52 55f /azw ATTORNEYLE;

Aug. 1, 1967 J, T. MATTHEWS 3,333,81

ROCHER MECHANISM Filed Sept. 1965 4 Sheets-Sheet INVENTOR ATTORNE Aug.1, i967 1. T. MATTHEWS HOOKER MECHANISM 4 Sheets-Sheet 5 Filed Sept.

INVENTQ BY f,

/ idd@ www( 60u/ ATTGRNEYS A118- 1 1957 J. T. MATTHEWS 3,333,8H

HOOKER MECHANISM Filed Sept. 1965 v4 Sheets-Sheet L Y @mi IWENTOR@mm/Waff ww' ATTORNEY United States Patent O 3,333,811 RGCKER MECHANISMJohn T., Matthews, Charlotte, N.C., assignor to Wil-Mat Corporation,Charlotte, N.C., a corporation of North Carolina Filed Sept. 7, 1965,Ser. No. 485,188 14 Claims. (Cl. 248-376) The present invention relatesto new and novel rocker mechanism, and more particularly to rockermechanism for use with chairs or seat structures.

The rocker mechanism of the present invention is par ticularly adaptedfor use with chairs or seats such as office chairs and the like. Therocker mechanism is so designed as to normally bias the mechanism into adesired neutral position and to facilitate rocking movement when sodesired by a person occupying the structure supported by the rockermechanism itself.

In order t accomplish these desired results, the rocker mechanism of thepresent invention incorporates a unique structure wherein a plurality ofsupport arms are pivotally connected -With a base means, and a supportframework is operatively associated with the support arms, the supportframework including pivotally supported side member means for supportinga seat or the like. The base means, the support arms and the supportframework are preferably formed of a rigid metallic material so as toprovide a very strong and durable construction.

Unique resilient means is operatively associated with the rockermechanism so as to normally bias the over-all mechanism into a neutralposition. This resilient means may take different forms, and in variousmodifications of the invention, compression spring means, tension springmeans and torsion spring means as well as certain combinations of thesespring means are employed.

A special advantage of the arrangement of the rocker mechanism of thepresent invention is the fact that it can be utilized with diiferenttypes of base means. This enables maximum versatility since the supportarms can be pivotally supported on any suitable type of base means andany conventional supporting leg arrangement. In particular, the rockermechanism of the present invention may be associated with a base meanswhich is a swivel arrangement so that the over-all combination providesa swivel rocker which is highly desirable in oiice chairs or similararticles of furniture.

The construction of the present invention isquite compact, employs aminimum of parts, is relatively inexpensive to manufacture andsubstantially trouble-free in operation. At the same time, thearrangement is quite sturdy and rugged in construction so as to readilywithstand loads applied thereto in normal use.

The support framework connected with the support arms of the structureenables any suitable means to be supported on the rocker mechanism, andin a typical example a seat structure is shown as supported on thesupport framework, although it will be understood that any othersuitable means may be supported thereon if so desired.

An object of the present invention is to provide new and novel rockermechanism which is particularly adapted for use with chairs or seatssuch as oliice chairs and the like.

Another object of the invention is the provision of rocker mechanismwhich may be employed with dilerent types of supports and which can beparticularly combined with a swivel base means to provide a swivelrocker arrangement.

Still another object of the invention is to provide rocker mechanismemploying novel resilient means to bias the mechanism to a neutralposition and to facilitate rocking movement when in use.

3,333,811 Patented Aug. l, 1967 A further object of the invention is toprovide rocker mechanism which is quite compact, employs a minimum ofparts, is relatively inexpensive in construction, is substantiallytrouble-free in use, and yet which is quite sturdy and rugged andreliable in operation.

Other objects and many attendant advantages of the invention will becomemore apparent when considered in connection with the specification andaccompanying drawings, wherein:

FIG. 1 is a top view of a first form of the invention;

FIG. 2 is a rear view of the structure shown in FIG. l;

FIG. 3 is a side view of the structure shown in FIG. 1;

FIG. 4 is a top View of a modilied form of the invention;

FIG. 5 is a rear view of the structure shown in FIG. 4;

FIG. 6 is a side view of the structure shown in FIG. 4;

FIG. 7 is a bottom perspective view of an oliice chair employing thestructure shown in FIGS. 1 3 inclusive;

FIG. 8 is a sectional view taken substantially along line 8-8 of FIG. llooking in the direction of the arrows;

FIG. 9 is a sectional view taken substantially along line 9-9 of FIG. 3looking in the direction of the arrows;

FIG. 10 is a sectional view taken substantially along line 10-10 of FIG.3 looking in the direction of the arrows;

FIG. ll is a sectional View taken substantially along line 11--11 ofFIG. 2 looking in the direction of the arrows;

FIG. l2 is a side View of a further modification of the invention;

FIG. 13 is a side view of still another form of the invention;

FIG. 14 is a top view of a still further modified form of the invention;

FIG. l5 is a rear view of the structure shown in FIG. 14;

FIG. 16 is a side view of the structure shown in FIG. 14 with a partthereof broken away for the sake of clarity; and

FIG.- 17 is a top perspective view of a portion of the structure shownin FIGS. 14-16 and partly broken away to illustrate the manner ofmounting one of the torsion springs of the structure.

Referring now to the drawings wherein like reference charactersdesignate corresponding parts throughout the several views, a tirstmodification of the invention is illustrated in FIGS. 1-3 and 7-11inclusive. In this modification, the base means is indicated generallyby reference numeral 10 which includes a swivel means indicated byreference numeral 12 and supported by a plurality of leg members 14shown as being four in number and each being of a generally channelshaped configuration. Suitable glide members 16 or other well knowntypes of support members can be employed with the leg members forsupporting them on a support surface.

The swivel means 12 may be of a construction as shown for example inU.S. Patent No. 2,779,642 and as particularly illustrated in FIG. 9 ofsuch patent. The swivel means includes a pair yof plates 20 and 22, thelower plate 20 being suitably secured to the leg members 14 as by nutand bolt assemblies vindicated by reference numerals 24. The plates 20and 22 are shown as being of generally square coniiguration, althoughany suitable shape may be employed. The plates are provided with corneropenings, the nut and bolt assemblies 24 extending through the corneropenings in plate 20 and suitably aligned openings provided inthe legmembers.

The plates 20 and 22 are provided with bearing races or channels 20a and22a respectively, these channels re- 3 ceiving a plurality of bearingballs 28 which are maintained in suitable spaced relationship by a cagestructure as set forth in the aforementioned patent.

A plate 30 of circular configuration has a downwardly facing annularraceway which receives va plurality of bearing balls 32, plate 30 aswell as the plates 20 and 22 all being held in operative relationship bymeans of a rivet stud 34 and a collar or washer 36, the upper end of thestud being-swaged over to hold the assembly in the assembledrelationship shown in FIG. 8. Y

The base means includes a pair of base members 40 and 42 each of whichis of channel-shaped configuration, being open at the top and defining across sectional configuration which is generally rectangular. The twobase members 40 and 42 are fixed in spaced relationship to one anotheron the upper plate 22 and may be secured in position by suitablefastening means such as rivets 40a and 42a respectively which extendthrough openings provided in the corners of the plate 22 and suitablealigned openings provided in the base members.

Support arm means comprises four separate and independent support armsindicated by reference numerals 50,52, 54 and 56, each of these armsbeing of generally channel-shaped cross sectional configuration and ofsimilar construction. The two support arms 50 and 52 are pivotallysupported by base member 40, the arms being vmounted for pivotalmovement about pivot pins 50a and 52a respectively, and the other twoarms 54 and 56 are pivotally supported by base member 42Afor pivotalmovement aboutY pivot pins 54a and 56a respectively. Since theconstruction of each of the arms is identical, and the manner ofpivotally mounting each ofthe arms is similar, a description of theparticular manner of mounting one of the arms will suffice for all.

Referring now to FIG. 10, the manner. of pivotally supporting arm 50 isillustrated. The opposite leg portions of the channel-shaped arm 50 areprovided with inwardly directed integral flange portions 60 and 62 whichsnugly receive and support bearing members 64 and 66 which may be formedof any suitable non-friction material such as nylon or the like. Thesebearing members 64 and 66 each have a central bore formed therethrough,the bores in the bearing members being aligned with holes 68 and 70provided in the opposite leg portions of the channelshaped associatedbase member. It is apparent that the pivot pin 50a extends through the-aligned holes and bores and serves to pivotally support the support armon the associated base member.

Spring support members 74 and 76 as seen most clearly in FIG.V 1 aresupported at an intermediate portion of the base members40 and 42respectively, these spring support members serving to support thesprings hereinafter described. Y

The various support arms 50, 52, 54 and 56 include laterally extendingportions 80, 82, 84 and 86 respectively which are adapted to engage thespring members associated therewith for biasing the support arms in aparticular direction. The construction of each of theserportions 80, 82,84 and 86 is the same, and accordingly, a detailed description of one ofthem will suffice for all.

VReferring now particularly to FIG. 11, the laterally extending portion86 of arm 56 includes a downwardly facing Vcup-shaped portion 88 whichreceives the upper end of a compression spring 96, the lower end of thiscompressionspring being retained Within a cup-shaped portion 77, securedto member 76. It is apparent that this arrangement will securely retainthe compression spring in operative position, and the compression springwill normally tend to bias the support arm 86 in a clockwise directionas seen in FIG. 1l about the pivot axis defined by pivot pin 56a.

Similar springs 90, 92 and 94 are operatively associated with the armportions 50, 82 and 84 respectively, it being understood ineach casethat the upper end of Yeach of these separate compression springs isreceived and retained in a downwardly facing cup-shaped portion, thelower end of each of the springs being received in a cup-shaped retainerprovided on one of the spring support means 74 or 76. With thisarrangement, each of the support arms is biased in a particulardirection about its associated pivot axis.

As seen in FIG. 3, it will be understood that arm 50 will be biased in aclockwise direction as will the arm 54 immediately therebehind in thisview, while arm 52 and the arm 56 immediately therebehind in this viewwill be biased in a counterclockwise direction as seen in thisparticular figure.

As seen most clearly in FIG. l, the support framework supported at theupper end of the support arms includes a first pair of frame members 100and 102. Each of these members is of tubular construction and may forexample be generally square in cross sectional configuration. Framemember .100 is rigidly secured as by welding or the like to the upperends of the arms 50 and 54. The frame member 102 is rigidly secured tothe upper ends of arms 52 and 56. Y

The opposite ends of thetubular members 100 and 102 are closed by capmembers 100a and 102a respectively, these cap members serving as meansfor pivotally supporting the side members 104 and 106 of the supportframework. It will be noted that each of members 104 and 106 ispivotally connected at spaced portions thereof with the two framemembers 100 and 102. Since the construction of the Vpivotalinterconnection -between each of the frame members and each of the sidemembers of the support framework is identical, a description of t-hedetailed construction of one will suffice for all. Y

Referring particularly to FIG. 9, a support stud includes a cylindricalshank portion 110 extending through a suitable opening provided in capmember a, and having formed thereon an enlarged head 112 which issuitably secured as by welding to the innerV surface of the cap member.The associated side member 104 is provided with an integral flangeportion 114 which defines a bearing portion which snugly receives theshank portion 110. It is evident that this arrangement provides apivotal interconnection between the side member and the associated framemember.

As seen most clearly in FIGS. l, 3 and 7, side member 104 is providedwith a plurality of spaced holes 116, and side member 106 is providedwith a plurality of spaced holes 118, these holes being employed forsecuring a suitable means thereto which is to be supported by the rockerstructure. As shown in FIG. 7, the means supported on the rockermechanism comprises a chair structure indicated generally by referencenumeral and including a seat portion 122 and a back rest portion 124. Itwill be understood that the seat portion 122 is suitably secured to theside members 104 by suitable fastening means as is conventional in theart. It will also be noted in FIG. 7 that one of the leg members hasbeen removed for the sake of illustration.

' Referring now to FIGS. 4 through 6 inclusive, a modified form of theinvention is illustrated, and in this form of the invention, the basemeanssupport arms, and support framework are substantially identicalwith the previously described modification and have been give the samereference numerals primed. The only difference in the construction shownin FIGS. 4 through 6 inclusive is in the provision of additionalresilient spring means for urging the rocker mechanism into a neutralposition and for facilitating the rocking action when in use. It will benoted that in this latter modification, four compression springs areemployed just as in the previously described modification.

In addition to the same structure as employed in theV support a pin 134at the outer ends thereof. A pair of bracket members 136 secured to arm54 support a pin 138, and a similar pair of bracket members 140 securedto arm 56 serve to support a pin 142 at the outer ends thereof. Y

A first tension spring 144 has the opposite ends thereof secured to pins132 and 134, and a second tension spring 146 has the opposite endsthereof connected to pins 138 and 142. It is apparent that these tensionsprings will tend to pull the associated arms toward one another and incooperation with the aforedescribed compression springs will bias therocker structure to a neutral position and assist in maintaining aproper rocking action when in use.

Referring now to FIG. 12 of the drawings, a still further modified formof the invention is illustrated, parts similar to those shown in FIG. 6having been given the same reference numerals. A comparison of FIG. 12with FIG. 6 of the drawings reveals that substantially the identicalconstruction is provided with the exception that in the modifiicationshown in FIG. 12, the two projecting portion 82 and 86 and theassociated compression springs 92 and 96 have been eliminated in thisform of the invention. In other words, the construction shown in FIG. l2is identical with that shown in FIG. 6 except that in the modificationshown in FIG. 12, the compression springs normally biasing arms 52 and56 in a counterclockwise direction have -been eliminated.

The other spring means employed in the modification shown in FIG. 12 areidentical with those shown in FIG. 6, or in other words a pair ofcompression springs 90' and 94 are provided for normally biasing arms50' and 54' in a clockwise direction about the pivot pins thereof and apair of tension springs 144 and 146 serve to bias arms 50 and 52 toward`one another and arms 54 and 56 toward one another respectively.

Referring now to the modification shown in FIG. 13, it will be notedthat here again the structure is similar to those previously describedin that the base means, the support arm structure and the supportframework are substantially identical with the first describedmodification. The parts shown in FIG. 13 similar to those shown in FIG.12 have been given the same reference numerals. In the structure shownin FIG. 13, the only difference from that shown in FIG. 12 is the factthat all of the compression springs have been eliminated so that thesole resilient means provided in ths form of the invention is thetension spring means 144 and 146. In other words, in the modificationshown in FIG. 13, a first tension spring is provided for biasing arms 50and 52' toward one another, and a second tension spring is provided forbiasing the other pair of arms 54 and 56 toward one another.

This resilient biasing means as employed in FIG. 13 will also serve tobias the support arms and the rocker structure to a neutral position andwill facilitate rocking action when in use as `in each of the previousmodifications.

Referring now to FIGS. 14 through 17, a still further modified form ofthe invention is illustrated. In lthis modification as in the others,the base means, the support arm structure and the support framework issubstantially identical with the first described form of the inventionand similar parts have beeny given the same reference numerals primed.In this latter modification, a modified form of spring means is employedwherein torsion springs are utilized for biasing the rocker mechanism toa neutral position and for assisting in providing the proper rockingaction.

A first torsion spring 150 is provided, and as seen particularly in FIG.17, the lower end of the torsion spring is secured within base member40' by means of a clamping member 152. An angle member bracket 154 issecured to the upper end of the torsion spring.

Bracket member 154 includes a first leg 156 having an integral offsetportion 158 which receives the upper end of the torsion spring. A secondleg member 160 is provided with a hole 162 therethrough for securing thebracket member to a suitable portion of the seat structure or the likewhich is supported on the framework.

A second torsion spring has the lower end thereof secured to the basemember 42 by means of a clamping member 172.

An upper bracket 174 is similar to bracket 172 and includes a first legportion 176 having an integral offset portion 178 for receiving theupper end of the torsion spring. A second leg portion 180 has a hole 182formed therethrough for securing the bracket member to a suitableportion of the supported seat structure or the like.

It is apparent that the torsion springs in this modification Willfunction in a manner so as to accomplish the same purpose as thecompression springs or tension springs in the previously describedmodifications in biasing the rocker mechanism to a neutral position andassisting in providing a proper rocker action when in use.

It is apparent from the foregoing that there -is provided according tothe present invention new and novel rocker mechanism which isparticularly adapted for use with chairs or seats such as Yoffice chairsand the like. It will be noted as seen for example in FIG. 3 that whenthe rocker mechanism is in its neutral position, the forward orright-hand portion of the support framework will be disposed slightlyabove the rear or left-hand portion of the framework such that theover-all support framework slopes from the rear portion thereof upwardlytoward the forward portion thereof. This provides the usual desiredneutral position of the associated chair structure. The resilient meansin each form of the invention serves to bias the rocker mechanism to itsneutral position so that the support framework is in the desiredrelationship, and the resilient means will facilitate proper rocking ofthe structure when in use. It is apparent that the rocker mechanism ofthe present invention can be employed with different types of supports,and is particularly adapted for use with a swivel structure to give aswivel rocker arrangement. The rocker mechanism is quite compact,employs a minimum yof parts, is relatively inexpensive to manufacture,is substantially trouble-free, and yet at the same time is quite sturdyand rugged and reliable in operation.

As this invention may be embodied in several forms without departingfrom the spirit or essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, and since thescope of the invention is defined by the appended claims, all changesthat fall within the metes .and bounds of the claims or that form theirfunctional as Well as conjointly cooperative equivalents are thereforeintended to be embraced by those claims.

I claim:

1. Rocker mechanism comprising base means including a pair of basemembers disposed in fixed spaced relationship to one another, fourseparate and independent support arms, a pair of support arms beingpivotally interconnected at the lower ends thereof with spaced portionsof each of said base members, a support framework connected with andsupported by the upper ends of said support arms, said support frameworkincluding pivotally supported means for connection with means to besupported, and spring means for biasing the rocket mechanism to aneutral position, said spring means being operatively connected Witheach pair of support arms interconnected with one of said base members,each of said spring means being disposed between the associated pair ofarms.

2. Apparatus yas defined in claim 1 wherein each of said spring means issupported by one of said base members at a point disposed between thepivotal interconnection of the lower ends of the associated arms withthe associated base member.

3. Apparatus as defined in claim 2 wherein said spring means associatedwith each of said pairs ofl support arms comprises a pair of compressionsprings, each of said compressions springs engaging portions on thelower part of one of said arms for biasing the associated arm in onedirection about the pivotal interconnection thereof with the associatedbase member. Y Y

4. Apparatus as dened in claim 3 including tension spring meansconnected between the arms of each of said pairs of .arms above saidcompression spring means operatively connected with the associated arms,said tension spring means normally tending to bias the upper ends ofsaid arms in a direction opposite to that in which the arms are biasedby the associated compression spring means.

5. Apparatus as defined in claim 1 wherein said spring means includescompression spring means operatively associated witheach of said pairsof support arms, each of said compression spring means being supportedby the associated base member between lthe points of pivotalinterconnection of the associated pair of support arms with theassociated base member, each of said compression spring means engaging aportion on the lower part of only one of the arms of the associated pairof support arms, said spring means also including tension spring meansconnected between the arms of each pair of support arms for biasing theupper ends of the arms of each of said pairs of support arms toward oneanother.

6. Apparatus as defined in claim 1 wherein said spring means comprises atension spring means operatively connected between the arms of each ofsaid pairs of support arms for biasing the upper ends of the arms ofeach of said pairs of support arms toward one another.

7. Apparatus as defined in claim 1 wherein said spring means comprises apair of torsion spring means, each of said torsion spring means-havingone end thereof connected with and supported by one of said base membersat a point between the pivotal interconnections of the associated pairof support arms with the associated base member, the opposite end ofeach of said torsion spring means being connected with said supportframework.

8. Rocker mechanism including base means, a plurality of separate andindependent support arms each of which is pivotally supported by saidbase means, resilient means for biasing the rocker mechanism into aneutral position, and a support framework supported by each of saidsupport arms, said support framework including a first pair of framemembers rigidly connected with said support arms, said yframeworkincluding a second pair of members each of which is pivotallyinterconnected with each of said frame members.

9. Rocker mechanism including base means, a plurality of separate andindependent support arms each Aof which is pivotally .interconnectedwith said base means, resilient means for biasing the rocker mechanisminto a neutral position, there being at least four support arms, asupport framework supported by said support arms, said support frameworkincluding a pair of frame members each of said frame members beingvrigidly connected with a pair of support arms, said framework alsoincluding a pair of side members each of which is pivotally connected atspaced points thereof with said pair of frame members.

10. Rocker mechanism comprising base means includ- -ing a pair of basemembers disposed in fixed spaced relationship to one another, foursupport arms, two support arms being pivotally connected with spacedportions of one of said base members, two other support arms Vbeingpivotally connected with spaced portions of the other of said basemembers, resilient means for biasing said Vrocker mechanism into aneutral position, a support framework connected with and supported bysaid support arms, said support framework including a first pair'offrame members, each of said frame members being rigidly connected withthe upper ends of a pair of said support arms, said support frameworkincluding a pair of side members, each of said side members beingpivotally interconnected a-t spaced points thereof with said framemembers. Y

11. Apparatus as dened in claim 10 wherein each of said frame members isrigidly interconnected with a support arm pivotally interconnected withdifferent ones of said lbase members. Y

12. Rocker mechanism comprising base means including a pair of basemembers disposed in fixed spaced relationship to one another, fourseparate and independent support arms, a pair of support arms beingpivotally connected with spaced portions of each of said base members,four separate compression spring means, each of said compression springmeans being disposed between said base means and one of said supportarms for normally biasing each support arm in one direction about thepivot axis thereof, a support framework connected with and supported bysaid support arms, said support framework including a rst pair of framemembers each of which is rigidly connected with a pair of said supportarms, said support framework including a pair of spaced side memberseach of which is pivot-ally connected at spaced portions thereof withsaid pair of 4frame members.

13. Rocker mechanism comprising base means including a pair of basemembers disposed in fixed spaced relationship -to one another, fourseparate and independent support arms, a pair of support arms beingpivotally interconnected with spaced portions -of each of said basemembers, four separate compression spring means, each of saidcompression spring means being disposed between said base means and oneof said arms for normally biasing each of said -arms in one directionabout the pivot axis thereof, and a pair of tension spring means, eachof said tension springmeans being connected between the support armspivotally supported by one of said base members, a support frameworkincluding a first pair of frame members each of which is rigidlyconnected with a pair of said support arms, said support framework alsoincluding a pair of side members each of which is pivotallyinterconnected at spaced portions thereof with said frame members.

14. Rocker mechanism comprising base means including a pair of basemembers disposed in iixed spaced relationship to one another, fourseparate and independent support arms, a pair of support arms beingpivotally interconnected with spaced portions of each of said basemembers, a pair of torsion spring means, each of said torsion springmeans being connected with one of said base members and being adapted tobias the rocker mechanism into a neutral position, and a supportframework connected with and supported by said support arms, saidsupport framework including a pair of frame members each of which isrigidly connected with a pair of said support arms, said supportframework including a pair of side members each of which is pivotallyinterconnected at spaced portions thereof with said frame members.

References Cited UNITED STATES PATENTS 208,08'3 9/187'8 Gorrell 24S-376X 399,502 3/ 1889 Davis 248--399 X 733,450 "7/ 1903 Wolf 248-389 X2,015,974 10/ 1935 Stannard 248-399, X y2,273,286 \2/ 1942 RobertiMii-388 2,916,084 1\2/ 1959 Bottemiller et al. 248-389 3,070,642 12/1962 Babbitt 248-376 3,249,331 5/ 1966 Hampton 248-399 X ROY D. FRAZIER,Primary Examiner.

CLAUDE A. LE ROY, Examiner.

R. P. SEITTER, Assistant Examiner.

1. ROCKER MECHANISM COMPRISING BASE MEANS INCLUDING A PAIR OF BASEMEMBERS DISPOSED IN FIXED SPACED RELATIONSHIP TO ONE ANOTHER, FOURSEPARATE AND INDEPENDENT SUPPORT ARMS, A PAIR OF SUPPORT ARMS MEANSBEING PIVOTALLY INTERCONNECTED AT THE LOWER ENDS THEREOF WITH SPACEDPORTIONS OF EACH OF SAID BASE MEMBERS, A SUPPORT FRAMEWORK CONNECTEDWITH AND SUPPORTED BY THE UPPER ENDS OF SAID SUPPORT ARMS, SAID SUPPORTFRAMEWORK INCLUDING PIVOTALLY SUPPORTED MEANS FOR CONNECTION WITH MEANSTO BE SUPPORTED, AND SPRING MEANS FOR BIASING THE ROCKET MECHANISM TO ANEUTRAL POSITION, SAID SPRING MEANS BEING OPERATIVELY CONNECTED WITHEACH PAIR OF SUPPORT ARMS INTERCONNECTED WITH ONE OF SAID BASE MEMBERS,EACH OF SAID SPRING MEANS BEING DISPOSED BETWEEN THE ASSOCIATED PAIR OFARMS.